>Someone has a bad day, let's make it even worse by giving them a thumbs down, it's ridiculous.

So giving them a thumbs-down is bad, but filing a formal complaint is fine? That seems like an extreme escalation.

Maybe I'm far less cynical than others here, but as has been mentioned in other comments, I don't believe that people are going to down-rank people out of spite. And if you ask a broad question like, "Is this person a good teammate, yes/no?" and the person gets many no's...perhaps it's something to look into?

> So giving them a thumbs-down is bad, but filing a formal complaint is fine? That seems like an extreme escalation.

No, on the opposite. If a coworker is just a bit unpleasant but I'm forced to rate them, I'm more likely to rate them negatively for reasons I have no idea about (maybe their dog died or are taking new medicine or whatever).

If I'm not asked to rate them, I won't do anything, until it's grave enough I should intervene. In this case, I will contact them directly trying to understand them and solve the problem in an amicable way, without involving any external party. This helps in a vast majority of cases. Only in extremely rare cases, once in a few years, the problem becomes so grave that another person needs to be involved. In any case, giving anyone a thumbs down doesn't solve anything.